Bedding is a haven for dust mites, thousands of which can feed, breed, and live on a single gram of dust. Allergy-proof bedding -- covers for mattresses, pillows, and duvets -- are routinely recommended by allergists to prevent inhaling the dust that carries mite droppings, causing allergies and worsening asthma.

But it seems the allergy-proof bedding is not enough to prevent the symptoms associated dust mite allergies, according to two new studies in this week's edition of The New England Journal of Medicine.

Little Difference in Beddings

In the first study, British researchers gave 1,100 people with mild asthma either allergy-proof bedding resistant to dust mites or bedding not impermeable to allergens.

In the second study, Dutch researchers say that allergy-proof bedding did reduce exposure to dust mites better than other coverings in 280 patients with known allergies, but not enough to prevent or reduce allergy symptoms.

The take-home message of both studies: Allergy-proof bedding, which costs between $20 and $60, isn't necessarily a waste of time and money. But it's not enough by itself to make a difference.

You cannot use covers by themselves to avoid allergy-triggers, which is routinely done by patients with dust mite allergies, Roy Gerth van Wijk, MD, PhD, researcher of the Dutch study, tells WebMD. "I still advise covers as a part of an allergy control program, provided that patients are motivated to take other measures."

In other words, if you are allergic to dust mites, continue to use the covers, but make sure you also address the other dust-filled places in your environment where mites infest.

"By themselves, dust mite-resistant covers may not do much. But they can still be, and probably should be, used in combination with other strategies to control allergy and asthma," says New York City allergist Clifford W. Bassett, MD, FAAAAI, spokesman for the American Academy of Allergy, Asthma and Immunology. "You also need to remove clutter -- especially in the bedroom -- avoid carpets and upholstered furniture, and continue medication recommended by your doctor."

Other measures he recommends include regularly dusting or washing baseboards, walls, and floors, changing and laundering bedsheets weekly, and cleaning furnace and air conditioning filters.

"These studies are certainly not the final word," Bassett tells WebMD. "In my experience, patients who use dust mite-proof protective coverings do find them to be helpful. They're not a financial hardship for most people, and an ounce of prevention is always worth a pound of cure."

Continued

"Conceptual Errors"

Another expert, who wrote an accompanying Journal editorial to the two studies, tells WebMD that while both were well-conducted trials by respected researchers, they had "conceptual errors" in execution.

For instance, because the researchers didn't know which patients were specifically allergic to dust mites -- as opposed to other allergy-triggers -- they can't really measure the exact role of the coverings, says Thomas A.E. Platts-Mills, MD, PhD, of the University of Virginia Asthma and Allergic Disease Center in Charlottesville.

"And in one study, they recommended that both groups of patients regularly wash their bedding," he says. "If you're washing bedding regularly, covering the mattress as well only has a modest effect in reducing allergen exposure.

"It's as if the researchers handed out different mattress covers to people who weren't doing a lot of the other things that they should to prevent or control their condition," Platts-Mills tells WebMD. "That's almost like saying, 'If you are supposed to use an inhaler twice a day to control asthma, will it work as well if you use it only once?' The answer seems obvious."